1. Field of the Invention
The present invention relates to a rotation angle detector which is used, for instance, as a steering angle sensor for a motor vehicle, in particular to an improvement on the light-receiving unit.
2. Prior Art
A rotation angle detector which is generally called a rotary encoder is a device for measuring the rotation angle as a digital quantity. For implementation of the measurement a circular rotary disc is used having a number of slits which are arranged around the center of rotation with a certain interval between each adjacent slit, and a light source and a light receiving unit with the disc in-between so that, as the disc rotates, the light incident on the receiving unit from the light source is interrupted periodically.
As the light-receiving unit of a prior rotation angle detector, use is made of a photodiode array (PDA) in which a p.sup.+ diffused layer for insulating individual photodiodes is formed on an n.sup.- epitaxial layer of a silicon substrate, and photodiodes P.sub.0 to P.sub.9 each consisting of p-n junction are incorporated in the p.sup.+ diffused layer. Because of this, it is difficult to dispose the photodiodes P.sub.0 to P.sub.9 to form a precisionally dimensioned high density array. This leads to the problem that the accuracy of detection and the resolution of the brightness border line that is projected on the PDA are low. Further, if a finely prepared pattern is used in an attempt to increase the density, there arises a problem that the detected photocurrent becomes minute, lowering the detection sensitivity.